1. Field of the Invention
This invention generally relates to balloon catheters for forcibly expanding a coronary artery and for dispensing medications. More particularly this invention is directed to a balloon catheter capable of delivering medications and to a method of manufacturing such a balloon catheter.
2. Description of Related Art
Balloon catheters for expanding atherosclerotic lesions or stenosises are well known in the heart. Such devices include inflatable balloons disposed at the end of multi-lumen catheter shafts. A pressurizing fluid forced into the balloon through an inflation lumen expands the balloon into the surface of an artery to enlarge its cross section.
U.S. Pat. No. 4,994,033 to Shockey et al. discloses a variation on a balloon catheter that is designed to apply a liquid medicament or other substance to a stenotic lesion as the blood vessel is undergoing dilatation to facilitate the restoration and long-term maintenance of patency to the blood vessel. This particular catheter includes three concentrically arranged flexible plastic tubes and a pair of concentrically arranged expansion members located at the distal end of the tubes. The space between the outer wall of the inner tube and the inner wall of the intermediate tube is in fluid communication with the interior of the first expander member. The second space between the outer wall of the intermediate tube and the inner wall of the outer tube is in fluid communication with the interior of the second expander member. A plurality of minute holes are formed through the second expander member to permit the liquid medicament to be ejected from the second expander member while an inflation fluid is introduced into the lumen of the intermediate tube.
Essentially, the Shockey et al. patent discloses two concentric balloons with an annular chamber formed between the balloons for receiving a medication that then disperses through the outer balloon through a series of holes. Other devices for performing these functions also exist. For example, U.S. Pat. No. 5,207,644 to Strecker discloses a similar device in the form of an implantable infusion chamber; and U.S. Pat. No. 5,320,604 to Walker et al. discloses a pair of expander balloons spaced apart on opposite sides of a waist portion at the distal end of a catheter in which the waist portion includes an infusion section with a perforation in communication with a drug delivery lumen. U.S. Pat. No. 4,693,243 to Buras discloses a flexible, non-collapsible conduit system for directly administering topical anesthesia in which the conduit system is separately positioned about a cuffed endotracheal tube for a direct topical application of additional substances to tissues of the larynx. U.S. Pat. No. 5,295,962 to Crocker et al. discloses a drug delivery and dilatation catheter that includes a inflation balloon disposed about a catheter and a perforated drug delivery balloon disposed concentrically about the inflation balloon. The drug delivery balloon contains a plurality of delivery ports over some or all of the surface of the delivery balloon or alternatively comprises a permeable material. U.S. Pat. No. 5,049,132 to Shaffer et al. also discloses a balloon catheter with concentric balloons. In this patent the outer balloon has apertures or slits that permit liquid flow outwardly through the balloon.
Increasing the pressure applied at the proximal end of many of the foregoing balloon catheters for administering a medicant increases the flow rate through the apertures . With sufficient pressure, "jetting" occurs whereby a relatively high-velocity stream emerges from the balloon with enough momentum to damage surrounding tissue. As one solution to this problem U.S. Pat. No. 5,213,576 to Abiuso et al. discloses two concentric balloons in which a medicament is directed into a central balloon and escapes through apertures in the inner balloon that are offset from apertures in an outer balloon. Each of the apertures or ports is sized to permit medication delivered through the lumen to pass outwardly through the perforations of both balloons, but the offset nature of the apertures prevents jetting.
U.S. Pat. No. 5,318,531 to Leone discloses an alternative infusion balloon catheter in which a balloon carries a plurality of holes sized to permit medication to be delivered through a lumen to pass outwardly through the holes. The balloon also carries on an outer surface a substantially hydrophilic, tubular, microporous membrane that covers the holes to break up streams of flowing medication.
More recently, an alternative balloon catheter, called a channel balloon, has been developed for the treatment of vascular disease including the delivery of medication to a site. One embodiment of such a balloon is shown in U.S. Pat. No. 5,254,089 to Wang. This channel balloon comprises a hollow, inflatable, extruded medication delivery balloon at the distal end of the catheter. Like other balloons, the interior of the channel balloon is in fluid flow relationship with one of several catheter lumens to enable the balloon to be inflated. In this particular structure, however, the balloon has inner and outer walls and angularly spaced radial webs that define an array of longitudinally extending conduits between the walls of the balloon. Another lumen in the catheter shaft delivers medication to these conduits, and the walls of the balloon have a single aperture for allowing the release of the medication from each conduit.
In the particular embodiment shown in the Wang patent, each conduit has a single port formed by inflating both the balloon and the conduits with air and then pricking each conduit wall lightly with a pin until it deflates. It is also suggested that the conduits could be pierced with laser irradiation. Apertures in the range from 0.0025 mm to 2.5 mm are suggested as potential aperture sizes depending upon the viscosity of the medication being dispensed. Elongated slits and other alternative aperture shapes are suggested.
As the medicament being administered moves directly through the exterior wall from an individual conduit in this channel balloon, jetting from the single apertures can still occur. Moreover, forming apertures in the outer wall is more complicated in a channel balloon that it is in a concentric balloon structure. For example, with individual concentric balloons it is possible to laser drill holes through one balloon as an outer balloon while it is separated from the final catheter assembly and then to overlay the outer balloon on the inner balloon. With conventional laser drilling, the laser is energized for an interval that assures complete penetration of the material being drilled. In a channel balloon, however, that approach to laser drilling would require sophisticated controls designed to produce just sufficient energy during a single application of laser energy to drill the exterior wall without significantly penetrating or weakening of the inner wall. Otherwise the structural integrity of the entire channel balloon can be compromised. Instead, these single ports are formed by incremental pulsing of a laser beam so it removes only a portion of the exterior wall. As each laser pulse interacts with the exterior wall, reflections at the walls tend to produce uneven energy distributions across the hole being drilled. This process can form tabs of material that are weakly connected to the channel balloon. There is always a potential for such material to release and form debris that can block the channel or, in the worst case, exit with the medication into the patient. These and other criteria would require the implementation of complicated and unduly expensive manufacturing controls to adapt prior art procedures for avoiding jetting to an extruded channel balloon.